Aerial delivery is frequently used for transporting cargo quickly to areas of limited or hostile access, for example areas without the availability of nearby airports. At times, people in isolated areas, such as jungles, deserts, mountains, polar regions, combat zones, and the like are in need of essential supplies, including food and medical supplies, but are not within access to an airport at which a supply plane could land. In these instances, aerial delivery of cargo from in-flight aircraft may be the sole option. Aerial delivery systems involve the use of parachute systems to slow the descent and gently land the cargo platforms on the ground.
Similar parachute systems are utilized for recovery of aeronautical and astronautical vehicles, including rocket boosters, experimental aircraft and space capsules, returning back to the earth's surface from flights in the upper atmosphere or outer space.
In these aerial delivery and/or recovery systems, a series of parachute deployments is often used to progressively slow the descent velocity of the payload. Use of a series of parachute deployments is often necessary because the force and impulse on the suspension lines and straps of a main parachute (i.e., a parachute large enough to slow the cargo platform to an acceptable landing velocity) deploying at the terminal, free-fall velocity of the cargo platform or vehicle would be excessive, causing the parachute system to fail. Instead, the payload is typically slowed in a series of stages using subsequently larger parachutes.
A drogue parachute is typically deployed first from the parachute system. The drogue is a small parachute which can be easily deployed from its container by a tether attached to the launching cargo plane, by an easily deployed stored energy means such as a spring launched pilot parachute, and/or the like. As the drogue parachute is deployed and inflated, it moderately decelerates the suspended cargo platform, as well as orienting the cargo platform into a desirable upright attitude, without excessive strain on the slings and parachute canopy from which the cargo platform is suspended. At a desired point, for example after a pre-determined time period, the drogue parachute is released from the suspended cargo platform. The drag provided by the released drogue parachute is then utilized to pull and deploy a next, larger parachute. This next parachute may be the main parachute, or another intermediary parachute prior to another subsequent deployment of the main parachute, depending upon the size of the cargo platform and the design of the parachute system.
To accomplish this release, a drogue parachute and/or intermediary parachute is typically attached to the suspended cargo platform by a release mechanism. The suspended cargo platform is suspended from the release mechanism, typically by a series of suspension slings. The suspension slings help maintain the suspended cargo platform in a stable, level attitude. The number of suspension slings is often four, with one routed to each corner of a square or rectangular cargo platform supporting the suspended cargo. For larger platforms, a greater number of suspension slings may be used. The suspension slings may converge at a point above the suspended load to the release mechanism, located at the apex of a pyramid formed by the suspension slings.
The drogue parachute and/or intermediary parachute is often attached to the release mechanism by a single sling or riser. From the top end of this sling, a number of suspension lines radiate to the perimeter of the drogue parachute and/or intermediary parachute canopy.
A common release mechanism is a pyrotechnic cord cutter powered by an explosive or pyrotechnic charge. This mechanism utilizes the detonation of a small explosive charge to drive a cutting blade through the suspension sling. However, pyrotechnic cord cutters are typically usable only for relatively small-diameter cords. As the weight of a platform and payload increases, the size of the cord or strap between the parachute and payload platform increases. A pyrotechnic cord cutter for payloads above a moderate size becomes too large for practical handling, and incorporates an explosive charge too large and powerful for safe handling by personnel.